I'm a newbie here, but I've thought about the fabled "Vanagon syndrome"
quite a bit, partly because my '84 Westy did the bucking thing coming over
Tehachapi Pass in the middle of the night and put a fright into my wife and
me both...like, were we going to spend the rest of our lives in this
California desert town?

It strikes me as odd that there are so many "fixes" for what appears to be
the same problem. If in fact it is the same problem, this could only mean
that there are multiple causes for it operating at the same time. How could
one person's vacuum leak fix have the same effect as another person's
soldering in a capacitor in the AMM? Both seem to fix the same problem.
Doesn't make sense.

What I'm thinking is that the Vanagon syndrome is actually caused by two (or
more) faults happening simultaneously, and only when they sync up do you
have the bucking, loss of power, etc. This would explain why fixing one of
the problems would seem to fix the Vanagon syndrome. They need to operate
together to cause the syndrome.

For example, maybe the syndrome is caused by a faulty solder joint in the
ECU that, in combination with a weak ground, causes the intermittent
problem. Fix one OR the other, and you fix the Vanagon syndrome, because
it's caused only by the two things working together. This would explain both
the intermittent nature of the problem and the multiplicity of solutions
that you find browsing the archives here.

I fixed our car--I think--by wiring up a good ground web on the
engine/frame/ECU, replacing all vacuum hoses, installing the capacitor in
the air mass meter, and seriously cleaning the battery ground. Next step is
to reflow all the solder joints in the ECU. After 21 years, you can expect
some cracking, and even if you can't see it with the naked eye, it wreaks
havoc with the ignition system.

Coming from the world of Saab 9000's, I do know that bad solder joints in
relays make your lights, etc. go nuts, and often on an intermittent basis.
Ditto for questionable grounds.

Start with the cheap first, anyway.

Good luck.